Process for treating cellulose-containing materials and recovering substances used therein.



SUBSTANCES O. 6. STAGE. PROCESS FOR TREATING CELL'ULOSE CONTAINING MATERIALS AND RECOVERIN G USED THEREIN. APPLICATION FILED MAR. I4. 1918.

Patented Sept. 24,1918.

l A i A. m m MW I O S- 1 Q N AN. .M. In.

OLA GEORG STAGE, OF THREE RIVERS, QUEBEC, QANADA.

rzaocnss m- TREATING SfIBSTANQES USED THEREIN.

Specification of Letters Patent.

CELLULOSE-CONTAINIIQIG MATERIALS m) RECOVERING Application filed March l l, 1918 Serial No. 222,298.

To all whom it may concern: Be it known that I, OLA Gnonc STAGE,

I a subject of the King of Sweden, residing at Three Rivers, in the Province of Quebec and Dominion of Canada, have invented certain new and useful Improvements in Processes for Treating Cellulose-Containing Materials and Recovering Substances Used Therein,

of which the following is a specification.

The object of this invention is to more perfectly recover alkali and fuel in the sulfate cellulose process. To this end I make use of the improved steps iii said'process hereinafter more particularly set forth and claimed.

In the accompanying drawings Figure 1 represents a side elevation of a digester used in said process, with sundry tanks, pipes, pumps and valves coiiperating therewith, by means of which my invention is made effective; and

Fig. 2 represents a plan view of the same. Hitherto, in a sulfate mill operated for cellulose production the usual procedure has been as follows: 9'

First; the bark is removed from the wood which is to be pulped and this wood is cut into small pieces or chips. Sometimes it is dried before further treatment. The chips are fed into a digester or digesters, filling the same.

Secondly; the chips are cooked or digested in the digester by heat and pressure in the presence of a liquor consisting of a solution of sodium compounds, the most prominent of these being sodium hydroXid (NaOH), sodium sulfid (Na S), sodium sulfite, sodium carbonate (Na CO and sodium sulfate (Na SO,) the first two of these compounds being the active' agents. The heat and pressure may be supplied by the direct introduction of hot steam into the digester; but the same result is more indirectly effected by heating the liquor in a separate receptacle or heaterand introducing it thus heated and under steam pressure into the digester or using mechanical means such as umps to maintain a circulation of said liquor through the digester.

Thirdly; the digester is emptied of its contents, by blowing or dumping, into the wash tanks, where the pulp is separated from the black liquor.

Fourthly; this liquor is evaporated partly or wholly in heated evaporators, C

Fifthly; this liquor is incinerated in a rotary furnaceand then burned in a blast furnace, from which sodium carbonate in a. melted state runs out into a dissolving tank; or, if the black liquor be evaporated to Patented sept. 2a, 1918.

about 30 136., it is blown by compressed air directly into the blast furnace, dispensing with the rotary furnace and using for speedy intensification of heat additional light fuel such as wood oil and gas. But if the liquor be sufficiently overheated before entering the furnace, there will be no need for this extra fuel, but the remaining Water in the liquor will evaporate immediately. Sodium sulfate isadded to the furnace to make up for lost alkali. Superfluous heat may be directed to a boiler behind the blast furnace or rotary furnace.

Sixthly; if the solution in the dissolving tanks be sufficiently strong it may-be causticized, the sludge separated by settlin or filtering from the clear liquor and the latter is ready for use in the digesters.

The liquor which is pumped from the alkali room for use in the digester is called white (strong) 7 liquor. The first qliquor drawn ofi" from the digester after digesting is called strong black liquor;- and as the black liquor grows weaker in the washing process, the part of it which is drawn oii' later is called weak black liquor.

Besides such recovery of alkali and other materials by burning dissolving and subse-.

quent treatment, some mills treat the relief gases exhausted from the ddgSStGIS, and also the black liquor, to obtain turpentine resin oil and other by products for fuel and other uses. y

In carrying out my improved process, I prepare the wood chips and supply them as usual to the digester in the usual way,

using the indirect method of heating to obtain the liquor in the digester as heavy as possible.

In the accompanying drawings A and B designate operating pumps used in one convenient arrangement or system of the apparatus whereby my invention is carried into effect, D being the digester, E a tank for strong black liquor, Fa tank for weak black liquor and Ga tank forhot water, these tanks being of varying sizes in accordance with their several needs; thus tank E is the largest, tank G the next largest antitank F the smallest; but these proporp; Y net/aces tions are not absolute. The said tanks E i and G are respectively connected from their bottoms or points near the same by branch pipes e. f and g to, the main conduit C of the system, which is bent to extend from the bottom of the digester around to the top of the same. The pump A- is included in this conduit between the lower end thereof and branch pipe 6, and pump B is similarly included between branch pipe 9 and the higher end conduit C, the latter of course being divided into 5 pipe sections at these points to connect with the said pumps. Between digester D and pump A there is-a out off valve it, and similar. valves 2' lc are arranged respectively in conduit 0 between branch pipes .eand f and between branch pipes f and 9. Also there are similar valves Z, m, n inbranch pipes e fand 9 respectively. While the process goes on these various valves are of course opened or closed in such manner as to permit the va rious steps and procedures hereinafter described. The pumps'and valves are only conventionally indicated in the drawings.

After cooking or digesting, the liquor 'pump 18 will beoperated to pump weak lack liquorfor washing (preferably de,

rived from a previous operation) from tank F into the top of digester D. This use of weak black liquor to begin washinglinstead I of water) is for the purpose of obtaining as much of the strong black liquor as pos- Increased amount of strong black liquor requires the relatively great size of sible.

tank E already mentioned Also, pump A ,will be operated to transfer strong black liquor-from the bottom, of digester D into tank E. When the liquor is sufficiently weakened by these transfers, it is pumped into. tank I5, leaving the pulp in the digester free to be Washed clean. This final opera blOIl of washing, like the preceding washing by weak liquorfis not effected in an open wash tank or elsewhere under exposure to evaporation; but the hot water from tank G is pumped by pump into said dig-ester to thoroughly wash the pulp under heat and pressure. This action continues until-the pulp i thoroughly washed, when it is blown or dumped out of said digester in the usual way through outlet pipe 0 to the blow pit hence is E F G are constructed to withstand as greator other suitable receptacle,- this latter pipe being governedby a valve p of suitable bon struction.

Liquor is never'exposed to evaporation, rzept in closed-receptacles and their necessary tubular connections. The tanks pressure as the digester and their contents will have a temperature corresponding to that in the digester. l/Vhen a digester is charged for cooking or digesting,- liquor from tank E-is used, to get sufficient fluid in said digester, and as this liquor is cooking temperature, there is a gainon the time required for digestion, which Wlll offset the loss of this kind of service of the dlgester when the latter is in use for washing the liquor will evaporate instantaneously and the inflammable substances will catch fire. To save all such fuel as far as guard against open evaporation.

All evaporators, whether directly or indirectly heated, are dispensed With;

The superheated liquor'in tank E is a1 possible, I

lowed'to escape through the discharge pipe S, governed by a cut oil" valve 6, to a rotary furnace or blast furnace in the manner now practised as above described.

The methods already in use as above described for the regaining of materials, making the clear liquor again available and utilizing extra heat, are adopted and carried out in my impgoved process.

liquor is kept from the external air and it will be observed that by my process the under full digester pressure at all stages of l its treatment. Also that the pulp iswashed under pressure, and the efficacy of the treat ment i thereby greatly increased, both for cleansing the pulp and acting chemically on the liquor to recover the alkali and other materials, without "at any stage exposing said liquor to open evaporation. By means of such increased efiicacy in the latter in' stance, ll am able to dispense with evaporators, which would otherwise be needed, and

with means for heating and charging and I discharging the same. Thisis obviously an important gain; Also the work. of digestion is done more perfectly. Furthermore, there is advantage in having the pulp in the digester mixed with hot water only, before dumping, instead of being mixed with liquor, as it will be discharged with no waste of the latter in a purer state. During washing the pressure on thedigester will fall a little,

and the final dumping or blowing off will be effected in the usual way. The direct transof the black liquor fromthe digester, or the closely connected tank E under equal pressure, to the furnace where the material is burnt is a notable step in simplification andv improvement of the apparatus; It is also important to transfer the relief gases from the digester directly to the furnace, for use as fuelitherein, as they contain a considerable percei itage of inflammable hydrocarbone.

. e ss may therefore be briefly recapitulated as:

1. Washing the pulp under digester pressure. Y

*2. Emptying the di ester when the pulp b ervation of this liquor under digestive heat is mixed with water only. I v A 3. Keeping the black liquor under digester pressure all through the process.

4:. Leading the black liquor directly. from the digester to the furnace where said liquor is burnt.

5. Transferring relief gases from the digester as fuel to the blast furnace without escape of inflammable material.

Relief pipes t with cut off valves are used in the tops of tanks E and F also a similar pipe with safety valves 15 in the top of hot 4 water tank G.

Having thus described my invention, what I claim as new and desire to secure by' Let- 'ters Patent is:

1. In a process for treating cellulosecontaining materials and recovering substances used therein, the transferof black liquor from the digester to the means of burning under digester heat and pressure and without exposure to the air.

2. In a process for treating cellulose-containingmaterials and recovering substances used therein, the withdrawal from the digester of a part of the black liquor after its digestive action on said materlals, the substituti'm in the digester of weak li nor for the liquor thus withdrawn, the was ing of the pulp by the liquor in the digester thus weakened and the preservation of this liquor under digester heat and pressure in order that it may be subsequently transferred for burning without loss.

3. In a process for treating cellulose-containing materials and recovering substances used therein, the withdrawal from the digester of a part of the black liquor after its digestive action-onsaidmaterial's, the transferof said black liquor to means of burnmg, under digestive heat and pressure without exposure to the air, the substitutionof weak liquor in the digester for the liquor thus withdrawn, the washing of the pulp in the digester without exposure to the air by the liquor thus weakened and the presof such liquor under digestive heat and pres- I sure and without exposure to the air for subsequentburning'without loss, a final washing of-the pulp with hot water'underpressure and the dumping of the pulp from the digester-while mixed with water only.

'5. In a process for treating cellulose-con-. taining materials and recovering substances used therein, the withdrawal of a great part of'the stron black liquor from the digester after the igestive action on such materials, thesubstitution of weak black liquor therefor in the di'gester, the washing of the pulp by the liquor thus weakened in 'the digester, and the preservation of both the stron black liquor thus withdrawn and the weak black liquor under digestive heat and pressure and without exposure tothe air to avoid loss before burning.

In testimony whereof, I have signed my name to this specification in'the presence of two subscribing witnesses.

H opA GEORG STAGE.

Witnesses: y

AUG. Esrnrm, Eme LINDBERG. 

